The Health Commission of Hubei province, China, first announced a cluster of patients with atypical pneumonia of unidentified pathogenic cause on 31 December 2019.1 The virus was isolated; its genome was then sequenced by a number of Chinese scientists who confirmed it to be a type of coronavirus. The virus was named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the resulting disease was termed coronavirus disease 2019 (COVID-19) by the World Health Organization.2 The infectious disease centre at Princess Margaret Hospital, Hong Kong, is the designated local tertiary referral centre that provides treatment for patients diagnosed with COVID-19. Case reports available at the time of writing describe ground-glass lung changes in isolated patients with COVID-19.3 4 5 Herein, we evaluate the radiological features in the earliest group of patients with confirmed COVID-19 in Hong Kong. The aim of the present study was to provide insights into radiological identification and assessment of COVID-19 pneumonia.

Patients in this study were confirmed to have SARS-CoV-2 infection on the basis of a positive nasopharyngeal aspirate reverse transcription polymerase chain reaction result and/or a positive serological testing result. The first 20 confirmed patients from all hospitals in Hong Kong were sent to our infectious disease unit for quarantine and treatment.

The radiological images reviewed in this study were obtained with high-resolution computed tomography (CT) or conventional thoracic CT. The examinations were performed with a multi-slice 16-head detector scanner (LightSpeed; GE Medical Systems, Waukesha [WI], United States) in the infectious disease centre, which is equipped with a negative pressure ventilating system.

The following parameters were used for high-resolution CT of the thorax: voltage, 120 kVp; current, 30-300 mA (smart mA); field of view, 32-40 mm; and gantry rotation, 1.0 s. Conventional CT was performed with the following parameters: voltage, 120 kVp; current, 100-500 mA (smart mA); diagonal field of view, 40 mm; and gantry rotation, 0.5 s.

Radiographers who performed CT scans of patients with confirmed or suspected COVID-19 were required to wear full-body protective garments, in accordance with guidelines from infection control specialists. All radiographers wore disposable fluid-resistant gowns, gloves, face shields, face masks with a rating of at least N95 (3M; Aberdeen [SD], United States), disposable shoe wraps, and protective eyewear. Patients were also required to wear masks with a rating of at least N95. All surfaces in contact with or within 1 m of the patients were cleaned with antiviral agents after completion of scanning. Cleaning procedures were performed twice; subsequently, the CT suite was not used for at least 30 minutes to allow for several air exchanges prior to the entry of the next patient.

The radiological images were reviewed and interpreted by consensus; the reviewers were two consultant radiologists who were registered specialist radiologists under Hong Kong Medical Council, Fellows of the Royal College of Radiologists, and Fellows of the Hong Kong College of Radiologists with 20 years of experience each in body CT.

From 22 January 2020 to 29 February 2020, our hospital received 20 patients aged 25 to 80 years all with confirmed COVID-19 (Table). Chest radiographs were performed for all patients on admission; the most common finding was bilateral non-specific pulmonary infiltrates (Fig 1). Shortly after admission, 19 patients (11 men and eight women) underwent high-resolution CT or conventional plain CT thorax. One patient was asymptomatic and exhibited normal chest radiographs throughout the hospital stay; thus, no CT scans were performed for further evaluation. The median interval from confirmation of diagnosis to CT scanning was 3 days.

As indicated in the Table, ground-glass opacities (GGO) with peripheral subpleural distribution were observed in all patients (100%) [Figs 2, 3a, b]. Furthermore, 57.9% of the patients exhibited diffuse involvement of both upper and basal zones, 15.8% demonstrated upper zone predominance, and 26.3% demonstrated basal predominance. All lobes of the lungs were involved in 16 (84.2%) patients (Fig 2), subsegmental consolidative changes were present in 14 (73.7%) patients (Fig 3a, c), interlobular septal thickening was present in 12 (63.2%) patients (Fig 3a), bronchial wall thickening or dilation was present in 10 (52.6%) patients (Fig 3b), and crazy-paving patterns were present in six (31.6%) patients (Fig 3). Mediastinal lymph node enlargement (ie, short axis >1 cm), centrilobular nodule, and pleural effusion were not detected in any of the patients.

In summary, peripheral subpleural GGO without zonal predominance in the absence of centrilobular nodules, pleural effusion, and lymph node enlargement were consistent findings. Other common findings included septal thickening, consolidations, bronchial dilatation/wall thickening, and crazy-paving patterns.

The most common respiratory pathogens are viruses. The imaging findings of viral pneumonia are diverse and often overlap with the findings of other non-viral pneumonias and inflammatory conditions. Imaging findings have been described in recent outbreaks associated with emerging pathogens, including severe acute respiratory syndrome (SARS) coronavirus and Middle East respiratory syndrome (MERS) coronavirus.6 7 Although a definite diagnosis cannot be reached based on imaging features alone, recognition of viral pneumonia patterns can aid in identification of potentially infected patients, especially during a specific viral outbreak.

Peripheral subpleural GGO without zonal predominance in the absence of pleural effusion and lymph node enlargement were consistent findings in initial thoracic CT scans of patients with COVID-19. These findings coincide with recent reports of single patients in which the major findings comprised multifocal patchy GGO, most evident around the periphery.3 4 5 Several other findings including bronchial wall thickening, bronchial dilatation, septal thickening, and crazy-paving patterns were also observed in a subset of patients.

Similar to our findings, diseases caused by other β-coronaviruses (eg, SARS, MERS, and other endemic human β-coronaviruses including OC43 and HKU1) are also characterised by multifocal peripheral GGOs. Moreover, patients infected with those viruses rarely exhibit cavitation, lymphadenopathy, or pleural effusions,6 similar to the findings in the present study. However, our study showed that lung changes in patients with COVID-19 have no zonal predominance, which contrasts with the findings in patients with SARS or MERS, which predominantly affect basal zones.6 Air-space opacities are less frequent in patients with COVID-19 pneumonia, compared with patients with SARS or MERS, which suggests that the course of COVID-19 pneumonia may be less aggressive. Nonetheless, conclusions should not be drawn prematurely as this study only involved the initial radiological assessment. More insights into the temporal changes regarding radiological findings during the progression of disease will become available as these patients undergo follow-up scans. Further studies that include the clinical course of COVID-19 in these patients will be performed in the future.

Coronavirus disease 2019 is a highly contagious disease that requires high vigilance and rapid detection. Knowledge of common radiological patterns on CT thorax can help discern the extent of pulmonary involvement and potentially facilitate identification of patients with pneumonia in Hong Kong during the COVID-19 outbreak.

Concept or design: All authors.
Acquisition of data: All authors.
Analysis or interpretation of data: All authors.
Drafting of the manuscript: SK Li, FH Ng.
Critical revision of the manuscript for important intellectual content: SK Li, FH Ng.

All authors had full access to the data, contributed to the study, approved the final version for publication, and take responsibility for its accuracy and integrity.

The authors have disclosed no conflicts of interest.

We would like to express our gratitude to the Infectious Disease Team and “dirty team” physicians of Princess Margaret Hospital, Hong Kong, for their professional patient care and invaluable contribution to the understanding of a novel disease.

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

This study was carried out with approval from the Kowloon West Cluster Ethics Committee (Ref KW/EX-20-032(144-20)). The requirement for patient consent was waived by the committee.

1. Centre for Health Protection, Hong Kong SAR Government. CHP closely monitors cluster of pneumonia cases on Mainland. 31 December 2019. Available from: https://www.info.gov.hk/gia/general/201912/31/P2019123100667.htm. Accessed 1 Feb 2020.

2. World Health Organization. Clinical management of severe acute respiratory infection when COVID-19 is suspected. Interim guidance. 12 January 2020. Available from: https://www.who.int/publications-detail/clinical-management-of-severe-acute-respiratory-infection-when-novel-coronavirus-(ncov)-infection-is-suspected. Accessed 1 Feb 2020.

3. Chan JF, Yuan S, Kok KH, et al. A familial cluster of pneumonia associated with the 2019 novel coronavirus indicating person-to-person transmission: a study of a family cluster. Lancet 2020;395:514-23. Crossref

4. Medlinkcn.com. 武漢19-nCoV 肺炎影像學表現初探 [in Chinese]. Available from: http://www.medlinkcn. com/?id=138. Accessed 1 Feb 2020.

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6. Koo HJ, Lim S, Choe J, Choi SH, Sung H, Do KH. Radiographic and CT features of viral pneumonia. Radiographics 2018;38:719-39. Crossref

7. Franquet T. Imaging of pulmonary viral pneumonia. Radiology 2011;260:18-39. Crossref